Ah, I did see the T440P but there was something that put me off. Maybe I got the weight wrong (thinking it was much heavier than the T440). Or perhaps there was something in the service manual (which is fantastic, by the way) - awkward HDD upgrade or similar.
As an aside, the dual-batteries on the T440 are fantastic. Though you do need to remember to disconnect the internal one when doing any work inside the unit.
